How to Calculate Water Cement Ratio

Water cement ratio controls the strength, durability and water tightness of hardened concrete.

Based on Abram’s Law (D.A. Abrams, 1919) “the compressive strength of concrete is inversely proportional to the ratio of water to cement”

Too much water will weaken concrete after curing, and Little water is dense but causes difficulty in placement and workability of  concrete.

The present of water in a concrete is the most important, Its affect the strength of the concrete, the durability of the concrete

•         Use a maximum of .50 of water for the concrete is in freeezing or thawing in the moist condition  
•         Use a maximum of .45 of water for the concrete with severe or very severe sulfate condition

The strength of the concrete increase if it has smaller water cement ratio. A 45 percent water cement ratio most likely will arrive 4500 psi while 50 percent cement ratio will mostly arrive in 4000 psi compresssive strength of the concrete.

 The calculation  on how to determine the water cement ratio is just directly divide the total volume of water against the volume of the cement (water cement ratio is equal to the total volume of water over the total volume of cement) or You can use average water - cement ratio, 6 gallons per 40 kg bag of Cement.

Excessive water causes bleeding and laitance. 

• Bleeding (emergence of excess mixing water on the surface of newly placed concrete caused by settlement of solids within the mass)
•  Laitance (milky deposit containing cement and fine aggregate on the surface of new concrete combined with bleeding, overworking of mix or improper finishing).